Thick-walled containers having an inner diameter of more than a meter usually are closed by a cover and bolts arranged in a circle. However, it is convenient to provide a thread between the cover and the container for more uniform transmission of forces as known, for instance, with the double receptacle for the transportation and storage of radioactive substances according to German patent 36 20 737. As the lid is very heavy in correspondence with the thickness of the walls of the receptacle (it may weigh as much as several hundred kilograms) and as the thread has a very large diameter (about one meter or more) the screw-coupling must be carried out very sensitively. That makes it necessary to guide the lid centrally in the thread and to avoid tilting at all events. Furthermore, the first contacting between the flanks of the threads must be shockless. During the threading operation, finally, the lid must not be allowed to lie on the flanks of the threads with its own full weight since its high weight and the friction caused by it would damage the thread. These difficulties generally occur wherever one component of very great weight and provided with a thread is to be screwed into another component.
Up to now heavy lids or covers were simply held and guided by a crane. Therefore, the problems described above were not solved by any means.